The autoimmune nature of type I diabetes is well established, but the mechanisms through which the inflammatory reaction is initiated and sustained remain to be determined. We plan to investigate the role played by cytokines in the destruction of beta-cells in NOD mice in vivo. We proceed from the hypothesis that an initial cytotoxic insult to beta cells may result from endogenous production of IL-1 and/or TNF, produced in response to an incidental stimulus. This initial injury may lead to sensitization, and thereby result in a sustained autoimmune response. Each aspect of this hypothesis will be tested, through administration of inhibitors of IL-I and TNF synthesis to susceptible NOD mice, through administration of antibody antagonists of IL-I and TNF to NOD mice, and through administration of inducing agents or the cytokines themselves. The effect of the lps(d) mutation (which precludes IL-1 and TNF synthesis in response to a variety of inducing agents including LPS) upon the development of autoimmune diabetes will be studied by placing this gene on an NOD background in homozygous form. The production of IL-1 and TNF within freshly isolated islets obtained from mice with active insulitis will be directly measured. The production of the hormones in vivo will be studied indirectly, by producing transgenic mice capable of expressing a marker enzyme (CAT) in response to stimuli that elicit production of each of the cytokines. These approaches should allow us to determine whether cytokine production and insulitis are temporally correlated, and whether the in vitro sensitivity of beta-islet cells to the cytotoxic effect of IL-1, alone or in conjunction with TNF, has an in vivo correlate in the pathogenesis of autoimmune diabetes.